Desulfurization of distillate fuels



Patented Mar. 30, 1954 DESULFURIZATION OF DISTILLATE FUELS Robert C. Arnold, Chicago Heights, Ill., assignor to Standard Oil Company, Chicago, 11]., a corporation of Indiana Application June 23, 1950, Serial No. 169,914

7 Claims.

This invention relates to the treatment of straight-run petroleum oils for the purpose of reducing the sulfur content. More particularly the invention is directed to the treatment of heavy naphtha, i. e., a material boiling between 250-425 F., kerosene, diesel oil, furnace oil and heater oil, 1. e., a material boiling between 325 and 575 R, which oils contain organic sulfur compounds in amounts, on a total sulfur basis, varying from about 0.3 to about 1.5 weight percent. Collectively these straight-run petroleum oils are referred to herein as distillate fuels.

The presence of sulfur in hydrocarbon oils that are to be used in gasoline and diesel engines and in domestic type heating units is believed to be undesirable even though not proved as harmful. It is thought that gasoline should be less than 0.15 weight percent sulfur content and preferably less than 0.10% sulfur. Although the basi for the limitation is somewhat vague at this time, it is thought that fuels for domestic type heating units, both space heaters and furnaces, should contain less than about 0.4% and preferably less than 0.3% sulfur. Excessive amounts of aromatic hydrocarbons are undesirable in such fuels because of carbon depositing tendencies; those aromatics removable with small amounts of liquid sulfur dioxide appear to be particularly harmful in this respect.

It is known to treat sulfur and aromatic bear- 5 ing distillates with sulfuric acid but thi process has the serious drawback of degrading large amounts of oil into virtually valueless sludge. In some cases uneconomically large amounts of acid must be used to reduce the sulfur content to a satisfactory point. The dearomatization of kerosene with liquid sulfur dioxide also results in a lowering of the sulfur content of the raffinate oil, but does not remove a sufilcient amount of sulfur compounds, with a reasonable treating loss, to

meet strict specifications.

An object of this invention is to produce petroleum distillate fuel of sulfur content suitable for use in domestic type heating units and automotive engine and to produce an oil low in'sulfur and low in objectionable aromatic constituents for use in distillate fuels. A specific object of this invention is to provide a process for making satisfactory distillate fuels from straight run petroleum distillate containing objectionable are in the form of a high sulfur extract instead of a sludge.

I accomplish the above objects by treating a virgin high sulfur distillate fuel at a temperature between 20 C. and --i0 0., e. g., l C. with an amount of liquid S03 in the range of about 1% to 5% by volume (based on distillate) and with an amount of liquid S02 in the range of about to 80% by volume (based on distillate) for a time of contact in the range of about one to sixty minutes followed by separation of resulting phases and removal of S02 from each phase, the raiiinate phase preferably being caustic washed after S02 removal. For optimum results the amount of S02 should be in the range of 50-80% when S03 is 1%, -60% when S03 is 2%, 15-50% when S03 is 3% and 10-40% when S03 is 4%. Unlike the process of U. S. 1,791,941, my process is directed to desulfurization, the conditions are such as to produce an extract as a byproduct instead of a sludge, and the relative proportions of S02 and S03 are in that critical range which is required for obtaining an amount of desulfurization which is disproportionate to treating loss.

As illustrations of the results obtainable by treating a high sulfur virgin heater oil (obtained from West Texas crude) with liquid S02 and sulfur trioxide,

Figure 2 shows the amount of extract material removed by treatment with liquid S02 solvent alone and with liquid S02 plus certain amounts of sulfur trioxide.

Figure 1 shows the desulfurization obtained, as percent of the original sulfur content, by

treatment with liquid S02 solvent alone and with liquid S02 plus the amounts of sulfur trioxide listed in Figure 2.

The data for the figures were obtained by treating a West Texas virgin heater oil having the following inspections:

API 40.2 Sulfur (lamp) weight percent 0.73 ASTM Distillation:

IBP F 332 10% F 390 -F l- 502 Max l 548 (The sulfur content of yirgin heater oils from 3 The indicated amount of sulfur trioxide was dissolved in the indicated amount of liquid S02 and the solution was added to the raw oil in the separatory funnel. The funnel was shaken to obtain equilibrium and allowed to settle when the S02 layer containing aromatic and sulfur compounds was separated. The total contact time was on the order of 2-3 minutes. Shorter contact times may be used successfully but contact times up to 2 hours have been used; these long contact times tend to promote undesirable color in the raiiinaie oil. The separated raffinate was stripped t remove S02 and was washed with caustic solution and water. For example, when 28 volume percent of liquid S02 and 2 volume percent of liquid sulfur trioxide were added to 200 ml. of the high sulfur virgin heater oil distillate, a rafflnate yield of 91% was obtained having a sulfur content of 0.24 weight percent, corresponding to a 68% desulfurization. Using 28 volume percent of liquid S02 alone, the desulfurization obtained was only 28% with a raffinate yield of 96%.

West Texas virgin heavy naphtha with 0.32 weight percent sulfur was treated, at the same conditions as for the heater oil. experiments, with 96 volume percent of liquid S02 and 4 volume percent of sulfur trioxide to produce a 76% yield of rafiinate having 0.05% sulfur whereas 100 volumes of liquid S02 alone produced a 79% yield of raflinate having a 0.16% sulfur.

Figures 1 and 2 show that the addition of sulfur trioxide to the liquid S02 results in a remarkable and unpredictable improvement in desulfurization efficiency of the solvent, with a relatively small increase in extract oil loss. Thus at volume percent of S02 treatment, 6% of the distillate is lost to extract with only 29 desulfurization; when 3 volume percent of S02 is added to the 30 volume percent of S02,"

11% of the distillate is lost to extract and 80% of the sulfur is removed. This 180% improvement in desulfurization with only 85% increase i extract loss is very surprising.

The results on treating distillate containing fact almost within the error of the determination; however, the loss to extract did increase even though little further desulfurization occurred. The data show that no worthwhile improvement in desulfurization takes place as the amount of S02 approaches close to 80 volume percent when 1% of sulfur trioxide is being used. The point of maximum effectiveness of each increment of S02 decreases as the amount of sulfur trioxide used increases. At 2 volume percent of sulfur trioxide, no worthwhile improvement is obtained by using more than about 60 volume percent of S02; the maximum desirable amount of S02 at 3 and 4% of sulfur trioxide usage are about and 40%, respectively.

For a distillate fuel having a sulfur content much higher than the 0.7% example used herein, the maximum amount of sulfur trioxide needed may be more than 4% but not more than 6% even with a 1.5% sulfur content raw oil.

In order to obtain a heater oil of satisfactory sulfur content, 1. e., about 0.3%, about a clesulfurization is needed when the raw distillate contains about 0.8% sulfur. This degree of desulfurization is not attainable with liquid S02 alone without excessive losses of oil to extract and large treats of solvent. Figure 1 shows that this desulfurization can be obtained at 2% sulfur trioxide usage with about 20% of liquid S02 usage; at 3% sulfur trioxide usage with about 15% of liquid S02 usage; and at 4% sulfur trioxide with about 10% of liquid S02 usage. At a temperature of --20 0., the miscibility of S02 in heater oil distillate is about 10% by volume, so that at least enough liquid S02 must be used to obtain a raffinate and an extract phase.

While it is possible to obtain substantially complete desulfurization by this process, the added amounts of both S02 and sulfur trioxide necessary to achieve this result make such a low sulfur content distillate fuel uneconomic for its normal use. A commercial installation must balance the cost of sulfur trioxide and the cost of handling the S02 in arriving at the preferred operating conditions. When a distillate of Off-1.0% sulfur is the type of feed stock, my preferred operating conditions are 23 volume percent of sulfur trioxide and liquid S02 ranging between the amount necessary to obtain phase separation, i. e., on the order of 10 volume percent, and about 60 volume percent; the exact conditions will depend on the amount of desulfurization desired.

It is indicated that the amount of desulfurization is dependent on both the amount of sulfur trioxide and the liquid S02 and the character of the desulfurization curves indicate that probably this phenomenon is more related to both extraction and chemical reaction than either alone. It is possible that the sulfur trioxide reacts with the sulfur compounds not extractable by the particular amount of S02 employed to form materials that assist the solution of the sulfur compounds in the liquid S02. The formation of sulfonic compounds does not completely explain the phenomenon because experiments using liquid S02 and alkane sulfonic acids, specifically, methane sulfonic acid did not show any marked improvement over S02 alone. For example, under conditions as given above, high sulfur distillate was treated with 48 volume percent of liquid S02 and 3.3 volume percent of methane sulfonic acid 46% desulfurization was obtained with 7% extract loss. A treat of 48% of liquid S02 alone resulted in 41% desulfurization at an extract loss of 8% The extract obtained from my process does not resemble in any way the sludge that is ob tained by sulfuric acid treatment of an oil. The freshly separated extracts are tan-colored, mobile liquids which darken somewhat on standing. The extract from a run-18% liquid S02 and 2% sulfur trioxidewas quenched in ice water, caustic neutralized and steam distilled. The major portion of the extract came over as a light yellow liquid which contained 6% sulfur, had an API gravity of 20; the color of this distilled extract did not change appreciably during storage.

My invention is applicable to distillate fuels obtained by distillation of crude or non-cracked oils, i. e., virgin or straight-run distillates. Tests on high sulfur catalytically cracked gas oils indicate that a satisfactory product can be obtained only at the cost-of a large loss to extract. For

example, a 29 API cycl'e' stock from' fluid cata- In general my invention can be carried out in the conventional Edeleanu process equipment. While the preferred temperature of treatment is about -20 0., lower temperature or higher temperatures, up to ordinary room temperatures, can be used; but in all cases pressure sufiicient to maintain the S02 in the liquid state must be used. Temperature below about 20 C. are preferable in order to prevent undesirable side reactions between the oil and the sulfur trioxide and maintain the selectivity of the S02.

I claim:

1. A process of refining a high sulfur virgin petroleum distillate boiling between about 325* and about 575 E, which process comprises contacting said distillate at a temperature between about +20 and about 40 C. with an amount of liquid S02 from at least enough to form a separate extract phase to not more than about 40 volume percent, based on said distillate, and between about 1 and 5 volume percent of sulfur trioxide, based on said distillate, separating a raifinate phase from an extract phase, and recovering from said raiiinate phase a product oil characterized by a sulfur content markedly lower than that of said distillate.

2. The process of claim 1 wherein said distillate has a sulfur content of between about 0.3 and about 1.5 weight percent.

3. The process of claim 1 wherein said distillate is a heater oil.

4. The process of claim 1 wherein said distillate is a kerosene.

5. The process of claim 1 wherein said distillate is a diesel oil.

6. The process of refining a virgin petroleum distillate boiling between about 325 and about 575 F. and containing between about 0.3 and about 1.5 weight percent sulfur, which process comprises contacting said distillate with a preformed mixture consisting essentially of liquid $02, in an amount between about 20 and not more than about volume per cent based on said distillate, and sulfur trioxide in an amount between about 2 and about 4 volume percent based on said distillate, at a temperature of about 20 C. for a time of between about 2 minutes and about 2 hours, separating a raifinate phase from an extract phase and recovering from said ramnate phase a product oil having a sulfur content markedly lower than that of said distillate.

7. The process of claim 6 wherein said distillate is a heater oil having a sulfur content of between about 0.6 and about 1.0 weight percent.

ROBERT C. ARNOLD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,710,143 Black et al. Apr. 23, 1929 1,791,941 Steik Feb. 10, 1931 1,893,138 Gary Jan. 3, 1933 

1. A PROCESS OF REFINING A HIGH SULFUR VIRGIN PETROLEUM DISTILLATE BOILING BETWEEN ABOUT 325* AND ABOUT 575* F., WHICH PROCESS COMPRISES CONTACTING SAID DISTILLATE AT A TEMPERATURE BETWEEN ABOUT +20* AND ABOUT -40* C. WITH AN AMOUNT OF LIQUID SO2 FROM AT LEAST ENOUGH TO FORM A SEPARATE EXTRACT PHASE TO NOT MORE THAN ABOUT 40 VOLUME PERCENT, BASED ON SAID DISTILLATE, AND BETWEEN ABOUT 1 AND 5 VOLUME PERCENT OF SULFUR TRIOXIDE, BASED ON SAID DISTILLATE, SEPARATING A RAFFINATE PHASE FROM AN EXTRACT PHASE, AND RECOVERING FROM SAID RAFFINATE PHASE A PRODUCT OIL CHARACTERIZED BY A SULFUR CONTENT MARKEDLY LOWER THAN THAT OF SAID DISTILLATE. 